The disclosure of Japanese Patent Application No. HEI 11-130101 filed on May 11, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an electromagnetic drive valve and a method for controlling the electromagnetic drive valve that drives a valve body in opening and closing directions by drawing an armature through the use of electromagnets and, more particularly, to an electromagnetic drive valve that is suitable for optimal control of the waveform of an electromagnet-energizing current.
2. Description of the Related Art
A known electromagnetic drive valve (described in, for example, Examined Japanese Patent Application Publication No. HEI 7-111127) has a valve body that serves as an intake or exhaust valve in an internal combustion engine, an armature that cooperates with the valve body, and electromagnets disposed at opposite sides of the armature in the directions of displacement of the armature. The electromagnetic drive valve opens and closes the valve body by supplying an exciting current having a predetermined waveform alternately to the electromagnets at timing synchronous with the crank angle of the internal combustion engine.
When the valve body of an electromagnetic drive valve is driven in the opening or closing direction, external forces caused by the pressure in the cylinder, the sliding resistance on the bearing, and the like, act on the valve body, as external disturbances. The magnitude of such an external disturbance varies every operation cycle of the valve body. The xe2x80x9ctime delayxe2x80x9d of the start of displacement of the valve body, which is caused by an effect of surface tension of oil films existing on contact surfaces of the armature and the electromagnets, also varies every operation cycle of the valve body. Therefore, if an exciting current having a pre-set waveform is supplied to the electromagnets of the electromagnetic drive valve, an appropriate waveform of displacement of the valve body may not be obtained, depending on variations in the external disturbances and the time delay. For example, if an external disturbance that impedes the displacement of the valve body increases, the valve body may fail to reach a predetermined end of displacement. If such an external disturbance decreases, the displacement velocity of the valve body at the time of displacement to the predetermined end may become excessively high, thereby causing problems of an increased operation sound level of the electromagnetic drive valve and the like.
Accordingly, it is an aspect of the invention to provide an electromagnetic drive valve capable of always providing an optimal waveform of current to be supplied to electromagnets for driving an armature.
In order to achieve the aforementioned and/or other aspects of the invention, an electromagnetic drive valve in accordance with one embodiment of the invention includes a valve body that is movable between a first displacement end and a second displacement end based on a displacement request. Additionally, an electromagnet attracts an armature that cooperates with the valve body, and a current supply supplies a current to the electromagnet. Furthermore, a position detector detects a position of the valve body between the first displacement end and the second displacement end when the valve body is moved from the first displacement end toward the second displacement end, and a controller changes a waveform of the current to be supplied from the current supply to the electromagnet, based on at least the position of the valve body detected by the position detector.
The position of the valve body during a displacement is affected by changes of the time delay between the output of the displacement request and the start of displacement of the valve body and changes of external disturbances received by the valve body during the displacement. The kinetic energy applied to the armature changes if the waveform of the current to be supplied to the electromagnet is changed. Therefore, by changing the waveform of the current based on the position of the valve body, the electromagnetic drive valve is able to provide an optimal waveform of the current that compensates for the changes of the delay time or changes of external disturbances.
The aforementioned changes of the delay time and the changes of external disturbances also affect the elapsed time to the time point at which the valve body reaches a predetermined position, and the velocity of the valve body. Therefore, the electromagnetic drive valve may further include a time detector that detects an elapsed time to a time point at which the valve body reaches at least one position located between the first displacement end and the second displacement end, or a velocity detector that detects a velocity of the valve body.